Biological wastewater treatment for treating wastewater using microorganisms requires lower operating costs than chemical wastewater treatment using a large amount of chemicals. Therefore, biological wastewater treatment is suitable for treating a large scale of wastewater. In the biological wastewater treatment, an immobilization technique is usually utilized in order to improve an efficiency of a decomposing reaction of pollutants and retain microorganisms in a treatment tank.
A method for immobilizing microorganisms is classified into two groups of an adhering immobilization method for making microorganisms adhere to a carrier surface, and an inclusive immobilization method for embedding microorganisms inside a carrier. The adhering immobilization method may be easily utilized. In contrast, the inclusive immobilization method enables selection of a microorganism type to be immobilized, allowing an easy increase in the reaction efficiency of the desired microbial species with higher priority than other microbial species. Further, the inclusive immobilization method is more effective than the adhering immobilization method, when an immobilization method is applied to treatment of nitrogen-containing wastewater or refractory substance-containing wastewater in which wastewater treating microorganisms tend to slowly grow, or treatment of wastewater in a winter season and a cold district.
Generally, a resin based material and a gel based material are used for a carrier that immobilizes microorganisms. A representative resin based carrier includes celluloses, polyesters, polypropylenes and vinyl chlorides. Further, a representative gel based material includes synthetic polymer materials such as polyethylene glycols, polyacrylamides, polyvinyl alcohols, and natural polymer materials such as agar, carrageenan, and alginic acid.
A hydrous carrier obtained from a gel based material has good compatibility with microorganisms, excellent microorganism retention, density close to that of to-be-treated water. This profile enables the hydrous gel carrier to be suitable for the inclusive immobilization method.
A technique for applying hydrous gel to a carrier is disclosed, for example, in Patent Document 1. This technique applies hydrous gel to an immobilization carrier, in which the carrier is prepared by polymerization of an oligomer used for a microorganism immobilization carrier. The carrier has a main skeleton part formed of polyalkylene glycol, and a sub-skeleton part formed of a urethane bond and ethyleneoxy, or a urethane bond, ethyleneoxy and propyleneoxy.